The specific field of application referred to above dates back to relatively recent times. Consequently, there does not exist extensive literature regarding the generation of scrambling codes in a UMTS context. Of course, there exists an extensive literature on the generation of orthogonal codes for CDMA applications, in particular, in W-CDMA (wideband CDMA) systems. The corresponding mechanisms of generation are substantially comparable to the mechanisms of generating pseudorandom noise (PN).
In this connection, useful reference may be made to the following: Roger L. Peterson, Introduction to Spread Spectrum Communications, Prentice Hall; Esmael H. Dinan and Bijan Jabbari, Spreading Codes for Direct Sequence CDMA and Wideband CDMA Cellular Networks, IEEE Comm Magazine, 1998; and Savo G. Glisic, International Courses for Telecom Professionals, Course 879, 1998. With specific regard to applications in a UMTS context, reference may be made, for instance, to the document WO-A-01/05079.
In order to generate scrambling codes for UMTS applications, usually two Linear Feedback Shift Registers (LFSRs) are used. One is called X (first) and the other Y (second) and each one generates a binary m-sequence. The modulo-2 sum of the two sequences thus obtained is referred to as a Gold sequence. A code used for UMTS applications is a complex sequence made up of a pair of Gold sequences referred to as the I branch and the Q branch.
The approach described in the document WO-A-01/05079 envisages the generation of primary and secondary codes by using a masking section. The masking section is used only for generating the I branch, while the Q branch is generated by delaying the I branch. The fact of using a delay line for shifting the code involves an unacceptable latency. Also, implementation of the delay line proves to be a problem, and in fact, the document in question makes no mention of just how the desired immediate delay can be obtained.